The present invention relates to a plastic screw cap with pilferproof ring.
Such caps are already commercially available and comprise a cylindrical cup which is internally threaded in order to be screwed onto the top of the container (bottle). A so-called pilferproof ring is coupled to the rim of the tray by means of breakable bridges and is internally provided with engagement elements constituted by flaps which, when the cap is applied to close the container, engage below a retention collar of the container.
By unscrewing the cap, the flaps abut against the collar and retain the ring, while the consequent axial traction force breaks the bridges.
In conventional caps the problem is felt of ensuring that during application to the container the flaps can expand or otherwise deform to move beyond the retention collar of the bottle and then contract again below said collar, so as to allow the pilferproof ring to separate during unscrewing and clearly indicate that the container has been opened.
Currently commercially available caps suffer some substantial drawbacks which are due to the structure of the teeth and to the technical difficulties in providing them, also in view of the problems linked to the molding steps, particularly to the extraction of the caps from the mold.
U.S. Pat. No. 5,107,998 discloses a closure with a pilferproof ring having a radially inwardly directed flange and a plurality of internal flaps pivotally secured to the flange. The flaps, during positioning of the closure upon a threaded finish of a container engage a recess and during removal of the closure are pivoted to engage the upper surface of the flange.
The aim of the present invention is to provide a plastic cap which can substantially obviate the shortcomings of conventional caps.
This aim is achieved by a plastic screw cap for sealing a container having a threaded finish and a collar adjacent to said threaded finish, said cap comprising a cylindrical cup provided with an internal thread and with a pilferproof ring which is connected to the rim of the cup by means of a plurality of bridges which form a fracture line, said ring having a plurality of internal flaps which are inclined towards the bottom of the cup; characterized in that the pilferproof ring comprises a cylindrical wall, whose thickness is such that it is substantially flexible in a radial expansion direction, a rim which is connected to the rim of said cup by said bridges, and an opposite rim which is connected to an annular internal bead whose inside diameter is smaller than the inside diameter of said wall and whose thickness is significantly greater than the thickness of said wall; and in that a plurality of flaps protrude from the region connecting said flexible wall and said internal annular bead, said flaps having such a thickness as to acquire substantial rigidity with respect to radial stresses, so that during removal of the cap abutment of the flaps on said collar produces expansion of said bead at the region connected to said wall.